Metal ions have been implicated as cofactors in the strand scission of DNA for a number of antitumor antibiotics. Bleomycin, a glycopeptide antibiotic, is known to bind to and cleave DNA in a reaction that depends on the presence of ferrous ion and molecular oxygen, "Bleomycin: Chemical, Biochemical and and Biological Aspects"; Hecht, S. M., Ed.; Springer Verlag: New York, 1979; Sausville, E. A.; Peisach, J.; Horwitz, S. B. "Biochemistry" 1978, 17, 2740. Burger, R. M.; Peisach, J; Horwitz, S. B. "Life Sciences" 1981, 28, 715; and Lown, J. W.; Sim, S. F. "Biochem. Biophys. Res. Comm." 1977, 77, 1150. The antitumor agent streptonigrin is also capable of causing single strand breaks in DNA using oxygen and cuprous ion, Cone, R., Hasan, S. K.: Lown, J. W.; Morgan, A. R. "Can. J. Biochem." 1976, 54, 219. Recently, the 1-10 phenanthroline-cuprous complex has been shown to cleave DNA in the presence of oxygen, Sigman, D. S.; Graham, D. R.: D'Aurora, V.; Stern, A. M. "J. Biol. Chem." 1979, 254, 12269; Graham, D. R.: Marshall, L. E.; Reich, K. A.: Sigman, D. S. "J. Amer. Chem. Soc." 1980, 102, 5419: Marshall, L. E.; Graham, D. R.; Reich, K. A.; Sigman, D. S. "Biochemistry" 1981, 20, 244: and Que, B. G.; Downey, K. M.; So., A. G. "Biochemistry" 1980, 19, 5987, These examples involve the concept of using a DNA binding molecule to deliver a metal ion to the site of the DNA helix where activation of molecular oxygen results in cleavage of the DNA.
According to the present invention, we have discovered a class of new bifunctional molecules containing a DNA intercalator or DNA groove binder molecule linked to ethylene diamine tetraacetic acid. An example of our invention is the synthesis of a simple bifunctional molecule, methidium-propyl-EDTA (MPE) which contains the DNA intercalator, methidium or ethidium covalently bound by a short hydrocarbon tether to the metal chelator, ethylene diamine tetraacetic acid. In the presence of ferrous ion and oxygen, MPE has been discovered to efficiently produce single strand breaks and some double strand breaks in double helical DNA with lower sequence specificity than the naturally occurring enzyme, DNase I. The efficient and low sequence specific DNA cleaving ability of MP.Fe(II) afford a new synthetic tool for DNA and RNA manipulations superior to the naturally occurring enzyme DNase I. ##STR2## In the above formula R is methyl or ethyl.
The novel compounds distamycin EDTA.Fe(II), EDTA-distamycin.Fe(II), penta-N-methylpyrrolecarboxamide-EDTA.Fe(II), bis(EDTA-distamycin).Fe(II) and EDTA(bisdistamycin).Fe(II) are effective as sequence specific DNA cleavers.